REVIEW OF DYNAMICS OF DISTRIBUTIONAL CONTROL 433 



carried into lower latitudes by the shallower water movements, and the eggs are returned to high 

 latitudes by deeper, southward-flowing movements '. In so far, however, as E. superba is concerned, 

 it is to be observed that while some larvae, Calyptopes and Furcilias, are unquestionably carried north- 

 wards (and eastwards) in the surface stream, there is little evidence of any mass return of eggs from 

 northerly spawnings to higher latitudes at a deeper level. On the contrary, it seems, the eggs move 

 north (and east) from southerly spawnings and it is only the very early larvae, the Nauplii, Meta- 

 nauplii and some of the First Calyptopes, that are ever involved in a deep southerly return. As for 

 other Antarctic species little is yet known of their major movements. At least one of them, however, 

 E. crystallorophias, obviously cannot be included in such a simple circulatory scheme, it being strictly 

 neritic, never it seems, either in its larval or adult state, leaving the immediate vicinity of the Antarctic 

 continental shelf. For the rest, John, who has written at large on the distribution of the southern 

 species, makes no mention of a deep return of eggs, neither do Rustad nor Ruud. Fraser does mention 

 a ' deep distribution of E. superba eggs ', but he was referring to a gathering on the Antarctic conti- 

 nental slope in a region where there was no deep southward movement. Moore gives no particular 

 authority for the remarks I have quoted, he does not consult Fraser, nor in this profusely and widely 

 documented book does he refer to either Rustad or Ruud. 



Ekman (1953), although he does not mention a deep return of eggs, makes much the same sweeping 

 generalisation as Moore. Referring to the ' more important cold-water ' southern species, E. crystal- 

 lorophias, E. superba, E. frigida, E. triacantha and Thysanoessa macrura, he remarks, ' In these species, 

 as in Calanus acutus, the fully grown individuals live only in the surface water and are transported 

 with it towards the Antarctic Convergence, while the younger stages are probably returned by the 

 antarctic return current to the pack-ice where the population has its maximum concentration'. Of 

 these five species, however, again only one, E. crystallorophias, in view of the very high coastal latitudes 

 to which it is confined, could be said to have its maximum concentration in the pack, or at any rate in 

 very cold water, although even in this species, as (p. 75) in E. superba, association with the ice will 

 probably prove to be nothing more than a seasonal phenomenon. Of the others, so far as is known, 

 in E. superba at least, it is the larvae, from the First Calyptopis onwards, rather than the adults, that 

 are carried for vast distances in the surface drift, not necessarily, however, towards the Antarctic 

 convergence, but to the west in the East Wind zone and to the north and above all to the east in 

 the Weddell stream. E. triacantha (Fig. 157) to take another, is certainly not a cold water form, its 

 major concentrations are far from the pack and it does not live (Baker, 1959) only in the surface but 

 in its adult state alternates daily between the surface stream and the warm deep layer. As for E. frigida 

 and T. macrura the major movements of the adults and larvae have not yet been worked out, nor is it 

 yet known that the fully grown individuals of either species are confined to the surface stream. 



Or to quote Lucas (1956a) on the effect of currents and surface 'swirls' on the distribution of 

 drifting animals, 'The process is also important in the vertical plane; otherwise, for example, the 

 steady drift of cold surface waters from the Antarctic region would tend to depopulate it of plants 

 and surface larvae. Mackintosh (1934) has shown a classic instance in the life history of Euphausia 

 superba, whose surface larvae drift away in their earlier stages, but sink later to be carried by the 

 south-going sub-surface flow back to the Antarctic, where they mature and produce surface eggs'. 

 In his Distribution of the Macroplankton in the Atlantic Sector of the Antarctic, which Dr Lucas cites. 

 Mackintosh makes no such reference to the larval krill, nor does he in any earlier or later work. In 

 a lecture delivered before the Royal Society in January 1950 he refers briefly (Mackintosh, 1950), 

 to what my findings then seemed to show, namely, a massing of the adults at the surface, a sink- 

 ing of the eggs to a depth of 1500 m. or more and a subsequent rising of the newly hatched krill 

 in the course of which they got carried southwards to replenish the stocks in higher latitudes. 



51 I'M 



